This is an archived article and the information in the article may be outdated. Please look at the time stamp on the story to see when it was last updated.

PARADISE, Calif. — First, the good news: Heavy rain expected this week won’t just drench Northern California’s Camp Fire. It could also snuff out the risk of new wildfires for the rest of the year.

Now the bad news: Flash flooding, mudslides and rivers of debris could hit cities already devastated by the wildfire.

A flash flood watch is in effect Wednesday through Friday for the Camp Fire area, where 3 to 6 inches of rain are expected.

The rain will end “fire concerns for the winter,” said Robert Baruffaldi, a meteorologist from the National Weather Service’s Sacramento office.

But it could also make conditions treacherous for firefighters battling the Camp Fire, which has charred more than 151,000 acres and was only 70% contained as of Tuesday morning.

The inferno has already killed 79 people and destroyed 12,900 homes. And with hundreds of residents still unaccounted for, authorities fear the death toll could rise.

Evacuees may face flooding

Fire-weary residents in Butte County are preparing for a possible deluge.

Jennifer Debrunner is staying at the Butte County Fairgrounds in an RV loaned by a stranger. She told CNN affiliate KCRA that her family covered everything they own with a tarp.

Debrunner said she knows the rain will bring “a lot of mud, a lot of cold” to the area. But this Thanksgiving week, Debrunner said she’s grateful her family has a borrowed RV.

Cady Machado has been camping out in a Walmart parking lot with her husband and 9-month-old baby.

But due to the expected rain, Machado told CNN affiliate KTXL, she’s sending her child to her sister’s in Arizona.

As for herself and her husband?

“There’s a nice bridge with my name on it to go underneath where I won’t get flooded out with my husband,” she told KTXL.

The Red Cross and other aid groups have opened additional shelters for people and pets in the area, KCRA reported.

“We want to make sure those people who are staying in tents know that these spaces are available for them so they can get out of the elements,” said Shawn Boyd with the California Governor’s Office of Emergency Services.

Ash flows expected in Paradise

The first bout of heavy rain is expected to hit Butte County on Wednesday, bringing about an inch to Paradise — a town virtually wiped out by the Camp Fire.

The National Weather Service’s Baruffaldi said the rain could cause ash flows, or a slurry of ash swept away by rainwater.

A second rain system arriving Thursday night will likely bring 1.5 inches of rain to Paradise and up to 4 inches in places of higher elevation, Baruffaldi said. That means mudflows are a real threat.

Southern California is in danger, too

The Woolsey burn area is expected to get less than an inch of rain. But it’s still at risk of mudslides and minor debris flow from Wednesday to Thursday, the National Weather Service in Los Angeles said.

Mudslides are more likely in the Woolsey Fire area because fires in the southern part of the state tend to destroy vegetation roots, Baruffaldi said.

Officials in Ventura and Los Angeles counties are urging residents to prepare for the rain. Fire departments in both counties are making an emergency supply of sandbags available to the public at fire stations.

Almost 700 people are unaccounted for

In Butte County, authorities are scrambling to find 699 people who are unaccounted for from the Camp Fire.

That number keeps fluctuating as more residents are found safe.

Hundreds of deputies, National Guard troops, coroners and anthropologists are sifting through destroyed homes and scorched cars for human remains.

Boyd said the rain could help authorities find victims by ridding the air of dust.

“You get rid of the dust, these dogs have a better chance at pinpointing and following their nose to where there may be remains,” Boyd told KCRA.

Butte County is keeping a list of the people who are unaccounted for because of the Camp Fire. Sheriff and Coroner Kory Honea urged those who see their own names or the names of loved ones found safe to contact the sheriff’s office.

Wildfires lead to widespread health concerns

Even Californians who never saw the flames could be affected by the wildfires’ health hazards.

Smoke from the Camp Fire hangs heavy in parts of the state, forcing schools to close and shutting down some public transportation.

The air quality is so bad that San Francisco, Stockton and Sacramento became the world’s three “most polluted cities” Friday, according to Berkeley Earth, a nonprofit that aggregates data from air-quality monitoring sites, worse than hot spots in China and India.